These results come from a surprising new Dutch study that finds brain abnormalities are not all that uncommon.
It is not clear how alarming this is. Most abnormalities had not caused any symptoms, though some were potentially life-threatening.
But the findings may have implications for patients in the future: As more of these abnormalities are spotted with more sophisticated equipment during routine medical tests, some doctors may urge patients to have surgery or other treatment as a precaution. Or some patients may push doctors to fix the potential problem.
"It's very scary to learn there's something wrong in your head," said Dr. Aad van der Lugt, an associate professor in radiology at Erasmus MC University Medical Center in Rotterdam and a co-author of the study published in Thursday's New England Journal of Medicine
The study is based on MRI, or magnetic resonance imaging, scans of 2,000 healthy adults with an average age of 63. They were participating in a study to look at the causes and consequences of age-related brain changes. The new paper's findings were incidental to the main research.
Participants who needed additional evaluation or treatment were referred to specialists. None of the brain tumors spotted by the MRIs required surgery, the researchers said.
Scans are increasingly being used, raising the chances that abnormalities will be spotted. About 20 million MRIs are done worldwide each year on the head, according to GE Healthcare, which makes scanners.
Even so, physicians do not recommend routine MRIs to look for brain problems in the way that people now get mammograms or colonoscopies.
"There's no evidence that screening MRIs of the brain are valuable," said Dr. Carolyn Meltzer, chairman of radiology at the Emory University School of Medicine.
The Dutch scientists found that 145 people - or 7.2 percent - had some dead brain tissue caused by a loss of blood flow. These are sometimes called silent strokes and usually don't result in a loss of speech or motion.
However, a patient who has had a silent stroke may be more likely to have another, more serious stroke, said Dr. Greg Joseph, a Charlotte, North Carolina, neuroradiologist who is part of a doctors group that reads 100 brain scans a day. Finding silent strokes allows doctors to prescribe medications or other measures that could prevent future problems, he said.
Another 32 people in the study - or 1.6 percent - had brain tumors. All but one were non-cancerous, but even benign tumors can kill if they grow and shut down vital brain functions. Doctors sometimes treat these, or do annual MRI scans to watch for signs of growth.
Another 35 people - or 1.8 percent - had bulging blood vessels, called aneurysms. Blood vessels that burst can cause serious strokes. However, all but five aneurysms found in the study were small and not considered dangerous.
The Dutch participants were mostly white, middle class and healthy; whether the same brain abnormalities would be found in other groups of people is not known, the researchers said.
In brain scans to investigate headaches or other problems, it is not unusual to find a small percentage of unexpected abnormalities. But the new study - one of the largest of its kind which used a state-of-the-art MRI scanner - gives perhaps the best estimate of how often these occur in the general public, said Judy Illes, a University of British Columbia professor who has written extensively on the topic.
One person who is glad she had an MRI is Seattle physician Sarah Hilgenberg. Five years ago, as a 24-year-old medical student, she joined a study in which participants got an MRI brain scan in exchange for $40.
That afternoon, while peeling apples at her kitchen sink, she got a call saying a problem had been spotted. More tests revealed a spider web of blood vessels over an eye that doctors feared could burst. They placed a kind of glue in the blood vessels and then removed the tangle in surgery.
The risky treatment could have killed her, but she is fine now and did not want to live in fear of a fatal brain bleed.
"In the end, I feel very lucky that it happened," she said of the original scan.